cmd/trace-agent: cleanup code related to APM events. #506

AlexJF · 2018-10-25T12:44:25Z

Move most of the code dealing with event extraction into its own package and rename samplers to extractors.

Also, change most references of transactions into events following the documented nomenclature.

This sets the ground for #508

AlexJF · 2018-10-25T13:08:14Z

constants/sampling.go

+package constants
+
+// SamplingPriorityKey is the key of the sampling priority value in the metrics map of the root span
+const SamplingPriorityKey = "_sampling_priority_v1"


^ Regarding this file, I added this to fix some cyclic imports. Happy to move this somewhere else that also works 😄

Let's move it into model where it originally was before I plucked it out, as discussed.

gbbr

This is a really nice change. I've just added some suggestions (ideas) around naming and exporting/unexporting stuff.

gbbr · 2018-10-26T06:43:11Z

constants/sampling.go

+package constants
+
+// SamplingPriorityKey is the key of the sampling priority value in the metrics map of the root span
+const SamplingPriorityKey = "_sampling_priority_v1"


Let's move it into model where it originally was before I plucked it out, as discussed.

gbbr · 2018-10-26T06:43:31Z

event/extractor/analyzed.go

@@ -0,0 +1,52 @@
+package eventextractor


Let's just have one main package event, as discussed.

gbbr · 2018-10-26T06:44:30Z

event/extractor/analyzed.go

+
+// AnalyzedExtractor is an event extractor that extracts APM events from traces based on
+// `(service name, operation name) => sampling ratio` mappings.
+type AnalyzedExtractor struct {


I'd like to suggest calling it like this:

// ratioExtractor extracts APM events from traces based on `(service name, operation name) => sampling ratio` // mappings. type ratioExtractor struct {

What do you think? The word analysed was always a bit confusing to me. But maybe I'm misunderstanding something.

gbbr · 2018-10-26T06:45:58Z

event/extractor/analyzed.go

+
+// NewAnalyzed returns an APM event extractor that extracts APM events from a trace following the provided
+// extraction rates for any spans matching a (service name, operation name) pair.
+func NewAnalyzed(analyzedSpansByService map[string]map[string]float64) *AnalyzedExtractor {


If this is going back into a main event package, it will probably sound nice like this:

event.NewRatioExtractor

Unless you think "analyzed" is better for some reason, which is fine by me. I just don't understand why this word is used, given that it doesn't appear in the documentation. What was analyzed (past tense) ?

gbbr · 2018-10-26T06:46:22Z

event/extractor/analyzed_legacy.go

+
+// LegacyAnalyzedExtractor is an event extractor that extracts APM events from traces based on `serviceName => sampling
+// ratio` mappings.
+type LegacyAnalyzedExtractor struct {


Maybe this could also just be legacyExtractor?

gbbr · 2018-10-26T06:46:50Z

event/extractor/analyzed_legacy.go

+// LegacyAnalyzedExtractor is an event extractor that extracts APM events from traces based on `serviceName => sampling
+// ratio` mappings.
+type LegacyAnalyzedExtractor struct {
+	analyzedRateByService map[string]float64


Do we need the word "analyzed"? Could it maybe simply be "rateByService"?

gbbr · 2018-10-26T06:47:36Z

event/extractor/analyzed_legacy.go

+
+	// inspect the WeightedTrace so that we can identify top-level spans
+	for _, span := range t.WeightedTrace {
+		if s.shouldAnalyze(span) {


From here I take it that the word analyze is meant for the future, as in: should the backend analyze this? Right? In that case we can remove the word "analyzed" from all the structs, etc. Here it makes sense, on this method.

gbbr · 2018-10-26T06:48:29Z

event/extractor/disabled.go

+type DisabledExtractor struct{}
+
+// NewDisabled returns a new APM event extractor that does not extract any events.
+func NewDisabled() *DisabledExtractor {


This could just be NoopExtractor if you like, or NewDisabledExtractor (the longer version)

gbbr · 2018-10-26T06:50:35Z

event/extractor/extractor.go

+// Extractor extracts APM event spans from a trace.
+type Extractor interface {
+	// Extract extracts APM event spans from the given weighted trace information and returns them.
+	Extract(t model.ProcessedTrace, sampledTrace bool) []*model.APMEvent


I really like this! A lot! I think this is a great idea. For this reason, I'd like to make this the main interface to interact with this package. What do you think? This means:

Make all Extractor implementations (noopExtractor, ratioExtractor and legacyExtractor) unexported.

Keep all constructors exported (NewRatioExtractor, NewLegacyExtractor and NoopExtractor) and have them all return an Extractor focusing the documentation about how they work on top of each constructor.

I think this will give for a great package. Having this interface will make a lot of sense then.

One last thing here: is there any way we can get rid of the second parameter? Is it needed? Wasn't this trace already sampled at this point? Or, would it make sense to include it into the ProcessedTrace struct instead? I think in your follow-up PR there can be a middle value (no decision) where the trace has neither been considered nor disconsidered yet.

gbbr · 2018-10-26T06:51:31Z

event/extractor/extractor.go

+}
+
+// FromConf creates a new APM event extractor based on the provided agent configuration.
+func FromConf(conf *config.AgentConfig) Extractor {


I'm wondering if this is the place to have this? I'm a bit skeptical about passing around the AgentConfig. It always seemed to me that this config was meant for the agent itself only. Maybe this logic belongs in there? (currently cmd/trace-agent)?

gbbr

This is a fantastic clean-up. So much better! ❤️And thanks for fixing the sneaky problem with missing events for un-sampled traces.

Added some comments but none are important to me, just nits and praises.

Feel free to merge whenever you like, but when you do, please squash and use the PR title as the commit message.

gbbr · 2018-10-29T11:43:03Z

cmd/trace-agent/agent.go

@@ -191,7 +169,7 @@ func (a *Agent) Process(t model.Trace) {
 	ts := a.Receiver.Stats.GetTagStats(info.Tags{})

 	// Extract priority early, as later goroutines might manipulate the Metrics map in parallel which isn't safe.
-	priority, hasPriority := root.Metrics[sampler.SamplingPriorityKey]
+	priority, hasPriority := root.GetSamplingPriority()


gbbr · 2018-10-29T11:43:18Z

cmd/trace-agent/agent.go

@@ -65,7 +43,7 @@ type Agent struct {
 	// tags based on their type.
 	obfuscator *obfuscate.Obfuscator

-	sampledTraceChan chan *writer.SampledTrace
+	tracePkgChan chan *writer.TracePackage


gbbr · 2018-10-29T11:43:31Z

cmd/trace-agent/agent.go

 		defer watchdog.LogOnPanic()
 		// Everything is sent to concentrator for stats, regardless of sampling.
 		a.Concentrator.Add(pt)
-	}()
+	}(pt)


gbbr · 2018-10-29T11:44:08Z

cmd/trace-agent/agent.go

-			return
+
+		if sampled {
+			pt.Sampled = sampled


This can be both inside the if and outside. Doesn't really matter, right? 😄

gbbr · 2018-10-29T11:45:33Z

event/extractor.go

@@ -0,0 +1,11 @@
+package event


Would be nice to document this package. It'd provide a nice opportunity to explain what events are in APM.

gbbr · 2018-10-29T11:48:41Z

writer/trace_writer.go

-	Transactions []*model.Span
+// TracePackage represents the result of a trace sampling operation.
+//
+// If a trace was sampled, then Trace will be set to that trace. Otherwise, it will be nil.


These two lines seem like they would be destined above each of the fields in the struct below 😊

gbbr · 2018-10-29T11:49:50Z

writer/trace_writer.go

-type SampledTrace struct {
-	Trace        *model.Trace
-	Transactions []*model.Span
+// TracePackage represents the result of a trace sampling operation.


I'd add here (if you think it helps) that "A package can still be valid when Trace is nil if it contains Events. This happens when a trace wasn't sampled but events might have been."

gbbr · 2018-10-29T11:50:46Z

writer/trace_writer.go

+// If a trace was sampled, then Trace will be set to that trace. Otherwise, it will be nil.
+// If events were extracted from a trace, then Events will be populated from these events. Otherwise, it will be empty.
+type TracePackage struct {
+	Trace  *model.Trace


It feels so unusual for this to be a pointer (to a slice, which is already technically a pointer).

gbbr · 2018-10-29T11:51:09Z

writer/trace_writer.go

-	return s.Trace == nil && len(s.Transactions) == 0
+// Empty returns true if this TracePackage has no data.
+func (s *TracePackage) Empty() bool {
+	return s.Trace == nil && len(s.Events) == 0


I wonder why this wasn't len(s.Trace) == 0 but it's fine.

gbbr · 2018-10-29T11:51:42Z

writer/trace_writer_test.go

-func randomSampledTrace(numSpans, numTransactions int) *SampledTrace {
-	if numSpans < numTransactions {
-		panic("can't have more transactions than spans in a RandomSampledTrace")
+func randomSampledTrace(numSpans, numEvents int) *TracePackage {


s/randomSampledTrace/randomTracePackage/g

AlexJF commented Oct 25, 2018

View reviewed changes

gbbr changed the title ~~Cleanup code related to APM events.~~ cmd/trace-agent: cleanup code related to APM events. Oct 25, 2018

gbbr added this to the 6.7.0 milestone Oct 25, 2018

gbbr reviewed Oct 26, 2018

View reviewed changes

AlexJF force-pushed the alexjf/event-extractor branch 3 times, most recently from b07d45f to 20efb7e Compare October 29, 2018 08:49

Cleanup code related to APM events.

ff459b9

AlexJF force-pushed the alexjf/event-extractor branch from 20efb7e to ff459b9 Compare October 29, 2018 09:00

Reduce flakiness in *_writer_test.go as last retry might be missed.

f1e4559

gbbr approved these changes Oct 29, 2018

View reviewed changes

AlexJF and others added 2 commits October 29, 2018 13:17

Address comments.

50bcec9

event: corrected package level doc

66cd02a

gbbr force-pushed the alexjf/event-extractor branch from fe99e85 to 66cd02a Compare October 29, 2018 12:26

gbbr merged commit 45a5f37 into master Oct 29, 2018

AlexJF deleted the alexjf/event-extractor branch November 16, 2018 09:29

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cmd/trace-agent: cleanup code related to APM events. #506

cmd/trace-agent: cleanup code related to APM events. #506

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cmd/trace-agent: cleanup code related to APM events. #506

cmd/trace-agent: cleanup code related to APM events. #506

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